Latent heat storage and method for temperature control of an internal combustion engine

ABSTRACT

A latent heat storage for an internal combustion engine is described having a crystallizable storage medium for storing heat while utilizing the enthalpy of a melting procedure. The storage medium has a state of supercooled molten mass at ambient temperature. Furthermore, the latent heat storage includes a crystallization nucleus provider for providing a crystallization nucleus in the storage medium, in order to trigger a crystallization of the storage medium to release stored heat in the state of supercooled molten mass. Additionally, an internal combustion engine is provided having such a latent heat storage and a method for temperature control of an internal combustion engine. In a first step of the method, a crystallized storage medium is melted in order to store heat while utilizing the enthalpy of the melting procedure. The storage medium then cools down at most to the ambient temperature and forms a supercooled molten mass in the process. A crystallization nucleus in the storage medium is provided in order to trigger a crystallization of the storage medium to release stored heat in a defined way.

FIELD OF THE INVENTION

The present invention relates to a latent heat storage for an internal combustion engine, in particular in a motor vehicle, and a method for temperature control of an internal combustion engine using a latent heat storage.

BACKGROUND INFORMATION

Latent heat storages use the enthalpy of reversible thermodynamic state changes of a storage medium, such as a phase transition between a solid phase and a liquid phase, in order to store thermal energy in the form of latent, i.e., hidden, heat. When charging the content of conventional latent heat storages, special salts or paraffins are typically melted as the storage medium, which absorb a very large amount of thermal energy, the melting heat, for this purpose. Since this procedure is reversible, the storage medium discharges precisely this quantity of heat again upon solidification.

In motor vehicles, latent heat storages are used to store excess energy arising during the operation of the motor vehicle and to provide it again on demand, for example, during a cold start. In order to maintain the charge of the latent heat storage over a longer period of time and to avoid unintentional release of the stored heat, the storage medium must typically be kept above its melting temperature by complex thermal insulation.

German Patent Application No. DE 10 2007 045 163 A1 describes a latent heat storage for the internal combustion engine of a motor vehicle, in which a supercooled, oversaturated, recrystallizable solution is used as the storage medium, in order to thus be able to dispense with thermal insulation of the storage medium.

In order to remove the stored heat, the recrystallization is triggered by pulsed release of mechanical energy with the aid of an actuator which provides a pulse.

It is therefore desirable in an improved latent heat storage for a motor vehicle to be able to store thermal energy without complex thermal insulation over a longer period of time and to be able to remove it reliably at the desired point in time.

SUMMARY

Accordingly, an example latent heat storage for an internal combustion engine having a crystallizable and supercoolable storage medium is provided for storing heat while utilizing the enthalpy of a melting procedure. The typical melting temperature of the storage medium is between 30° C. and 120° C.

A storage medium is used, which has the state of supercooled molten mass at ambient temperatures of approximately −10° C. to 58° C. Complex thermal insulation is therefore not required in order to prevent the storage medium from recrystallizing at an undesirable time and unintentionally discharging the stored heat.

Furthermore, the latent heat storage includes a crystallization nucleus provider for providing a crystallization nucleus in the storage medium in order to trigger a crystallization of the storage medium to release stored heat in the state of supercooled molten mass.

Since the crystallization nucleus provider allows—in contrast to a sound or pressure wave of an actuator, for example—the recrystallization to be reliably triggered at the desired point in time through the targeted provision of a crystallization nucleus, the heat may be discharged in a defined way.

Under further aspects, the present invention provides an internal combustion engine having a latent heat storage according to the present invention and a method for temperature control of an internal combustion engine. In a first step of the method, a crystallized storage medium is melted, typically using existing waste heat sources of the vehicle.

The storage medium cools down, sometimes to ambient temperature, and is supercooled in the process. To release stored heat, a crystallization nucleus is provided in the storage medium, in order to trigger a crystallization of the storage medium.

According to one preferred refinement, the crystallization nucleus provider includes a separating device for preserving, thermally separated from the storage medium, the crystallization nuclei below the melting point. This allows a separated part of the storage medium to be preserved as the crystallization nucleus in the crystallized state, while—e.g., during operation of the internal combustion engine—the remaining storage medium is melted and thus charged with latent heat. The thermally separated crystallization nucleus may subsequently be reused for further use of the latent heat storage, so that energy for renewed production of a crystallization nucleus—e.g., by local supercooling of the storage medium—may possibly be saved.

According to another preferred refinement, the crystallization nucleus provider is designed to apply a thermodynamic potential variable to the storage medium in order to create the crystallization nucleus in the storage medium. The thermodynamic potential variable, such as temperature or pressure, is advantageously selected in accordance with the storage medium in such a way that conditions are set, at least in a local area of the storage medium, which reliably result in the spontaneous formation of a crystallization nucleus. This allows a particularly high reliability of the trigger mechanism of the latent heat storage, since it does not depend on a crystallization nucleus actually having been successfully preserved in a separating device, e.g., in hot ambient conditions. The crystallization nucleus provider preferably has a cooling device for the local cooling of the storage medium, which sets the statistically sufficiently reliable crystallization nucleus formation temperature of the storage medium. This is particularly simple and safe to implement, e.g., with the aid of a Peltier element or a cascaded arrangement of Peltier elements.

According to one preferred refinement, an internal combustion engine includes a latent heat storage according to the present invention, the storage medium being situated in the area of an oil sump of the internal combustion engine, at least partially on or below a resting oil level of the oil sump when the internal combustion engine is resting. In this way, the storage medium directly heats the lubrication oil of the internal combustion engine and thus decreases its viscosity during a cold start, which advantageously reduces the fuel consumption and the pollutant emissions of the internal combustion engine in the first minutes after the start. The storage medium is preferably situated at least partially above an operating oil level of the oil sump when the internal combustion engine is in operation. In this way, the part of the oil which is located in the oil pan close to the surface (of the resting oil level) when the internal combustion engine is resting is initially heated and typically first reaches the area of the internal combustion engine to be lubricated with the aid of an oil intake port.

According to one preferred refinement, the storage medium has a surface, over which oil, returning into the oil sump, flows when the internal combustion engine is operated. In this way, the storage medium is initially heated by particularly hot oil, which is directly from the area to be lubricated—e.g., the cylinders—of the internal combustion engine, before the returning oil mixes with the still colder oil (in particular shortly after the start of the internal combustion engine) in the oil sump. This allows the storage medium to be melted reliably again even during brief operation of the internal combustion engine and thus be charged. This surface is preferably inclined, so that the returning oil runs at sufficient speed over the surface and discharges a particularly large amount of its heat to the storage medium.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is explained in greater detail below on the basis of preferred specific embodiments and the figures.

FIG. 1A shows a schematic cross-sectional view of an internal combustion engine having a latent heat storage according to a specific embodiment.

FIG. 1B shows a cross-sectional view of a latent heat storage according to a specific embodiment.

FIG. 2 shows a schematic diagram of a coolant circuit of an internal combustion engine having a latent heat storage according to a specific embodiment.

FIG. 3 shows a schematic diagram of a coolant circuit of an internal combustion engine having a latent heat storage according to a further specific embodiment.

FIG. 4 shows a graph of the relationship of enthalpy and temperature in a latent heat storage material.

FIG. 5 shows a flow chart of a method for temperature control of an internal combustion engine according to a specific embodiment.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In the figures, the same reference numerals identify identical or functionally identical components, if not otherwise specified.

An internal combustion engine 102, which is shown in a schematic cross-sectional view in FIG. 1A, is implemented for exemplary purposes as a gasoline engine having four cylinders 101 situated in a crankcase 103. A crankshaft 140, which is driven by pistons 142 movable in cylinders 101, is mounted below cylinders 101 in crankcase 103. Crankcase 103 is open at the bottom and terminates at a circumferential lower edge 141. An oil pan 133 for receiving lubricating oil 118, which is required for the operation of internal combustion engine 102, is screwed onto lower edge 141 of crankcase 103 and closes crankcase 103 at the bottom. A depressed area inside oil pan 133 is designed as oil sump 110, in which lubricating oil 118 collects up to a resting oil level 112 when internal combustion engine 102 is resting.

An intake snorkel 128 is situated in oil sump 110, via which internal combustion engine 102 removes lubricating oil 118 from the oil sump during operation to lubricate cylinders 101 and crankshaft 140 (and other parts). The oil level in oil sump 110 sinks to an operating oil level 114, at which a flow equilibrium results with oil flowing back from the area of crankcase 103 to be lubricated.

Furthermore, a storage medium 104 of a latent heat storage body 100, which is enclosed by an envelope 120, is situated in oil sump 110. Envelope 120 is manufactured from a metal such as aluminum, for example, and preferably has a plurality of ribs 121, in order to achieve a large surface area of envelope 120 for increased heat transfer between storage medium 104 and oil 110 enclosing the outer surface of envelope 120. A similar ribbed structure or structure which conducts heat in another way may additionally be provided inside envelope 120. Latent heat storage body 100 is situated below resting oil level 112, so that it is completely enclosed by oil 118 in the resting state of the internal combustion engine. It is situated generally spread along the horizontal at approximately half of the height between resting oil level 112 and the bottom of oil sump 110, so that in the resting state, it divides lubricating oil 118 located in the oil sump into an area above latent heat storage body 100 and an area below latent heat storage body 100. During operation of internal combustion engine 102, an upper surface 116 of latent heat storage body 100 protrudes above the then prevailing operating oil level 114. Latent heat storage body 100 is supported on a high base 122 and a low base 123, so that upper surface 116 is designed to be slightly inclined in relation to the horizontal toward the lower end of intake snorkel 128. At the end facing away from intake snorkel 128, latent heat storage body 100 touches lateral wall 124 of oil sump 110.

A starting device, e.g., a Peltier element 108, is attached to the outer or inner side of wall 124 of oil sump 110 in such a way that it is indirectly or directly in contact with latent heat storage body 100, which faces toward wall 124 from the inside. Peltier element 108, which is mentioned as an example, is connected via two lead-in wires 138 to a control unit 130 of latent heat storage 100. Control unit 130 contains an activation unit 134 for activating Peltier element 108 and a request detector 132, which is connected in one application to an antenna 136 for a central locking system of a motor vehicle having internal combustion engine 102. Furthermore, request detector 132 is connected to an ignition lock unit 137 for starting internal combustion engine 102.

Storage medium 104 is designed as a salt hydrate, for example, whose properties are schematically illustrated in the enthalpy graph shown in FIG. 4. Melting temperature 500 of the storage medium is marked on horizontal temperature axis 520. If the crystalline storage medium is heated up to melting point 500 beginning from the left end of temperature axis 520, its enthalpy, which is plotted along a vertical enthalpy axis 522, grows by a first amount 515 of sensitive (i.e., perceptible) heat absorbed in the course of this heating. If further heat is applied, storage medium melts 400, it absorbing latent heat 512 at constant temperature at the melting point. If the storage medium is completely melted, further supply of heat results in the increase of the temperature beyond melting point 500, a further amount 514 of sensitive heat being absorbed in the course of this heating. If the melted storage medium cools down again, it also remains in a metastable state 504 of supercooled molten mass below melting point 500, until a temperature range 508 is reached in which—with sinking temperature—a spontaneous recrystallization 510 of the molten mass begins with increasing probability and latent heat 512 is discharged. If a crystallization nucleus is provided in the storage medium in state 504 of supercooled molten mass, the storage medium crystallizes 506 also above crystallization nucleus formation temperature 508.

A material is selected as the storage medium in which, on the one hand, melting temperature 500 is in a desired temperature range 524 of the lubricating oil and, on the other hand, metastable state 504 of supercooled molten mass extends over a substantial part of typical ambient temperature range 502, in which the internal combustion engine is operated. A suitable material in the case of internal combustion engines in motor vehicles, which are used in moderate climate zones, is sodium acetate trihydrate, for example, whose melting point 500 is at 58° C.

In regular operation of internal combustion engine 102 from FIG. 1A, operating oil level 114 results as described above, while hot oil returning from crankcase 103 runs over upper surface 116 of latent heat storage body 100. In this way—at typical driving distances—storage medium 104 is reliably heated above its melting point 500, so that it melts completely. If internal combustion engine 102, which may be assumed to be installed in a motor vehicle as an example here, is shut down and subjected to an ambient temperature of −15° C., for example, substantial parts of oil 118 flow back into oil sump 110. The entire internal combustion engine including oil 118 and storage medium 104 gradually cools down to the ambient temperature of −15° C.

For example, if a vehicle driver approaches the motor vehicle and triggers the central locking system via antenna 136, request detector 132 concludes therefrom that internal combustion engine 102 is soon to be used and relays a corresponding signal to activation unit 134. Activation unit 134 applies an electrical current to starting device/Peltier element 108 over an application period of time, activation interval, current intensity, and current direction being selected in such a way that the entire configuration is cooled down to the extent that crystallization is triggered with statistically high probability. The application period of time and the current intensity are established in accordance with demand by activation unit 134 with the aid of a temperature signal or an estimation of the temperature.

Starting device/Peltier element 108, including its supply lines 138 and control unit 130, act as one device for providing a crystallization nucleus in storage medium 104. Through local cooling of storage medium 104 down to or below crystallization nucleus formation range 508, a crystallization nucleus spontaneously occurs in the supercooled molten mass, from which entire storage medium 104 crystallizes in a chain reaction and releases the latent heat. Storage medium 104 heats the oil adjacent to storage medium 104 through envelope 120. If the vehicle driver now starts the internal combustion engine with the aid of ignition lock device 137, it initially draws in, via intake snorkel 128, the oil located above storage medium 104, which is heated most strongly due to the elevated location of storage medium 104 and the convection and has therefore the lowest viscosity. Complete mixing and uniform heating of all of the oil only occurs in later operation of the internal combustion engine.

The specific embodiment shown in FIG. 1A may be modified in manifold ways. Thus, for example, starting device/Peltier element 108 may alternatively be situated inside oil sump 110, directly on envelope 120 of storage medium 104, or in a feedthrough through wall 124 of oil sump 110. Instead of Peltier element 108 mentioned as an example or in connection therewith, starting devices may be used which apply a static pressure locally to storage medium 104, in order to set thermodynamic conditions under which a crystallization nucleus may form spontaneously.

FIG. 1B shows a latent heat storage in which crystallization nucleus provision device 106 has, instead of starting device/Peltier element 108 from FIG. 1A, a separating device 152 for preserving, thermally separated from storage medium 104, the crystallization nucleus typically below melting point 500. Separating device 152, which is situated in a feedthrough through wall 124 of oil sump 110 and envelope 120 of storage medium 104, includes as an example a pair of pliers which is formed from thermally insulating half shells 160, which are pivotable against each other around a pivotal point 190, and which, in the closed state, may separate and thermally insulate a separation space 156 filled with storage medium from the remaining storage medium 104. Half shells 160 are connected, via a drawbar 158 guided through pivotal point 190 and branch bars 159 pivotably coupled thereto, to an actuator 150, which is activatable by control unit 130.

During operation of an internal combustion engine having the illustrated latent heat storage, in general a part of storage medium 104 is stored in the crystalline state below the melting temperature of storage medium 104 in the space which is thermally separated by half shells 160, which are closed by a restoring spring 154. Separation space 156 may be thermally conductively connected to the space outside the internal combustion engine, for example, insofar that the temperature in separation space 156 does not reach the melting point even during continuous operation of the internal combustion engine.

If activation unit 134 of control unit 130 activates actuator 150 during a cold start, it exerts a tensile force on drawbar 158, so that half shells 160 open and bring the crystallization nucleus preserved in the separation space into contact with remaining storage medium 104, which is in the state of supercooled molten mass. As a result of this, the entire storage medium 104 crystallizes in a chain reaction and releases its latent heat. Even before the entire molten mass has passed into the crystalline state, the current supply to the actuator is interrupted, so that the restoring spring closes half shells 160 again, which are movable with little exertion of force in the molten mass, which is not yet completely crystallized. Closed half shells 160 again enclose crystals, separate them, and thermally insulate them from the remainder of the storage medium.

FIG. 2 schematically shows the cooling and heating circuit of a motor vehicle having an internal combustion engine 102, a radiator 202, a radiator thermostat valve 210, a heating heat exchanger 200, a heater thermostat valve 21, a main water pump 208, and an auxiliary water pump 209. Main water pump 208 may be coupled via a drive connection (not shown) or the like to internal combustion engine 102, while auxiliary water pump 209 may be driven by a separate electric drive motor. If internal combustion engine 102 is running but still cold, with closed radiator thermostat valve 210, substantial parts of coolant 206 initially flow via a line 212 and main water pump 208 directly back to internal combustion engine 102 for the purpose of heating it more rapidly. A cooling circuit 216 via internal combustion engine 102, radiator thermostat valve 210, radiator 202, and main water pump 208 becomes active as soon as coolant 206 has reached a temperature at which radiator thermostat valve 210 opens.

A heating circuit 214, which leads via internal combustion engine 102 and heating heat exchanger 200, is driven by main water pump 208 and optionally auxiliary water pump 209. A latent heat storage 100 is situated in heating circuit 214 between internal combustion engine 102 and heat exchanger 200 and may be bypassed by a latent heat storage valve 222 situated in parallel. Latent heat storage 100 contains a storage medium 104, which is traversed by meandering lines (not shown) of heating circuit 214, for example, so that when coolant 206 flows through the latent heat storage, heat is exchangeable between coolant 206 and storage medium 104 of latent heat storage 100. A starting device 108 for providing a crystallization nucleus in storage medium 104 is attached in indirect or direct contact with latent heat storage 100. A control unit 130 has a flow control unit 220 for regulating the coolant flow through latent heat storage 100, in addition to an activation unit 134 for the starting device.

Before a trip using the motor vehicle, triggered by the remote unlocking device or the ignition lock, for example, activation unit 134 initiates the crystallization by spontaneous formation of crystallization nuclei in the storage medium using starting device 108, e.g., through local supercooling of the storage medium. Latent heat storage valve 222 is simultaneously throttled/closed and the electric drive motor of auxiliary water pump 209 is turned on, in order to pump heated cooling medium 206 from latent heat storage 100 into heating heat exchanger 200 and/or internal combustion engine 102.

FIG. 3 shows a cooling and heating circuit of a further motor vehicle. In contrast to the specific embodiment from FIG. 2, heating circuit 214 has an exhaust gas heat exchanger 312, which is situated in a branch line 304 of exhaust system 300 downstream from a three-way catalytic converter 302. Latent heat storage valve 222, which is connected to flow control unit 220, exhaust gas heat exchanger 312, and latent heat storage 100 are situated together in series inside heating circuit 214, and in parallel to heating heat exchanger 200. The sequence of the parallel arrangement is only shown as an example here.

Butterfly valves 308, 306 are situated in each case in exhaust gas branch line 304 and in the section of the main line of exhaust system 300 running parallel thereto. These valves and a main circuit valve 310 in main circuit 216 are connected, like latent heat storage valve 222, to flow control unit 220, by which they may be activated in a coordinated way during operation of internal combustion engine 102.

The arrangement shown in FIG. 3 allows latent heat storage 100 to be heated to particularly high temperatures to melt storage medium 104. In this way, storage media having a particularly high melting point may be used, which discharge heat again at a correspondingly elevated temperature level. A further advantage is that even in the case of very short trips using the motor vehicle, during which the oil/cooling water circuit of the internal combustion engine does not completely heat up, storage medium 104 may be reliably melted to charge latent heat storage 100 due to the high temperatures in the exhaust system.

FIG. 5 shows a flow chart of a method for temperature control of an internal combustion engine of a motor vehicle, in which a crystallized storage medium is melted in a first step 400 in order to store melting heat. This is performed, for example, during travel utilizing excess waste heat. In following step 402, the storage medium cools down, possibly to ambient temperature, after the vehicle has been shut down. A supercooled molten mass of the storage medium forms at this point.

In step 403, a request signal of the vehicle driver, e.g., a remote unlocking signal, is received. In step 404, upon the request signal received in step 403, a crystallization nucleus is provided in the storage material in order to trigger a crystallization of the storage medium to release stored heat, e.g., to the lubricating oil and/or the coolant of the internal combustion engine. In step 406, a part of the storage medium is separated as a crystallization nucleus from the remaining storage medium and thermally insulated from the remaining storage medium, before it is in turn melted in step 400 by heating beyond the melting point. 

1-11. (canceled)
 12. A latent heat storage for an internal combustion engine, comprising: a crystallizable storage medium, to store heat while utilizing enthalpy of a melting procedure, which may have a state of supercooled molten mass at ambient temperature; and a crystallization nucleus provider to provide a crystallization nucleus in the storage medium to trigger a crystallization of the storage medium to release stored heat in a state of supercooled molten mass.
 13. The latent heat storage as recited in claim 12, wherein the crystallization nucleus provider has a separating device to preserve, thermally separated from the storage medium, the crystallization nucleus below a melting point.
 14. The latent heat storage as recited in claim 12, wherein the crystallization nucleus provider is designed to apply a thermodynamic potential variable to the storage medium in order to create the crystallization nucleus in the storage medium.
 15. The latent heat storage as recited in claim 14, wherein the crystallization nucleus provider has a cooling device for local cooling of the storage medium to a crystallization nucleus formation temperature below an ambient temperature.
 16. An internal combustion engine having a latent heat storage, the latent heat storage including: a crystallizable storage medium to store heat while utilizing enthalpy of a melting procedure, which may have a state of supercooled molten mass at ambient temperature; and a crystallization nucleus provider to provide a crystallization nucleus in the storage medium to trigger a crystallization of the storage medium to release stored heat in a state of supercooled molten mass; wherein the storage medium is situated in an area of an oil sump of the internal combustion engine at least partially on or below a resting oil level of the oil sump when the internal combustion engine is resting.
 17. The internal combustion engine as recited in claim 16, wherein the storage medium is situated at least partially above an operating oil level of the oil sump when the internal combustion engine is in operation.
 18. The internal combustion engine as recited in claim 17, wherein the storage medium has a surface, which is inclined and over which oil, returning into the oil sump, flows when the internal combustion engine is in operation.
 19. A method for temperature control of an internal combustion engine, comprising: melting a crystallized storage medium, which has a melting point above an ambient temperature to store heat while utilizing enthalpy of the melting procedure; cooling the storage medium down to at most an ambient temperature; and providing a crystallization nucleus in the storage medium to trigger a crystallization of the storage medium to release stored heat.
 20. The method as recited in claim 19, further comprising: separating the crystallization nucleus from the remaining storage medium before the storage medium reaches the melting point.
 21. The method as recited in claim 19, wherein the providing includes applying a thermodynamic potential variable including one of a temperature or a static pressure to the storage medium to create the crystallization nucleus in the storage medium.
 22. The method as recited in claim 21, wherein the thermodynamic potential variable is applied to the storage medium over an application period of time of 1 second to 60 seconds before or during a start of the internal combustion engine. 